It has long been known to produce food packages of different types from packaging laminates. One commercially viable method is to continuously unite the longitudinal edges of a web and thereby form the web into a tube which is thereafter filled and sealed and severed transversely of the longitudinal direction of the web so that a number of cushion-shaped individual packages are formed. Depending upon the mutual orientation of the transverse seals and depending upon subsequent final folding, these packages may be given different configurations. Examples of such configurations are the tetrahedral package which is marketed by Tetra Pak under the name Tetra Classic®. Another example of such a package is the brick-shaped package which is marketed by Tetra Pak under the name Tetra Brik®. This generic type of package is well-known both to persons skilled in the art and consumers and will not be described in greater detail here. The brief description, given by way of introduction, of the method of realising such packages is also well-known to a person skilled in the art and will not be described in greater detail either. Only those details of such a filling machine as are encompassed by the inventive concept as herein disclosed and an understanding thereof will be described in greater detail.
During the last decade, it has become increasingly common practice to provide, above all, the traditional, brick-shaped packages with different types of opening arrangements. One type of opening arrangement is described in EP 949 992 A1. This opening arrangement is realised in that a hole is punched through the packaging laminate, whereafter this hole is covered by an opening arrangement which is injection moulded straight over the hole. The injection moulding is put into effect in that a moulding tool is placed on either side of the packaging laminate so that the mould cavity formed by the moulding tools completely encloses the previously punched hole. By injecting hot, mouldable plastic into the entire mould cavity, the hole is sealed. This type of opening arrangement is normally formed with a weaker portion which extends about a greater part of the circumference of the opening arrangement so that a consumer may open the package by breaking a part of the opening arrangement along the weakening.
In order to realise such an opening arrangement, it is important to be able to place the hole punched in the web in the correct position in the injection moulding station. EP 1 110 867 A1 describes how it is possible to employ the hole as a reference point for positioning thereof in the injection moulding station. The traditional method prior to this was to employ some form of guide mark in order to position the packaging laminate web both before the punching operation and then before the injection moulding operation. One problem which may thereby occur is that a sum total is made of two error tolerances so that the opening arrangement is not injection moulded over the hole within its mutual tolerances. By measuring the position of the hole for positioning before the injection moulding, this tolerance accumulation chain has been eliminated.
EP 1 110 867 describes a set of three punches and three injection moulding stations where three mutually subsequent packaging blanks are punched simultaneously and three mutually subsequent packaging blanks are provided with opening arrangements by injection moulding simultaneously.
Recently, there has been an increasing demand for small packages, so-called portion packages, for example of the order of magnitude of 150 ml and upwards. One problem which has thereby occurred is that the distance between the hole positions of two mutually adjacent packaging blanks will be so slight that it is difficult to construct injection moulding units which can be positioned so close to one another. EP 1 249 399 describes how this problem has been solved by first punching, for example, every second packaging blank and thereafter indexing one step so that the other packaging blanks are punched. Once all packaging blanks which lie adjacent one another have been punched, a longer indexing is put into effect (for example five steps) so that all punched packaging blanks are conveyed past the punch units.
In connection with this type of indexing, with short and long index steps, it has nevertheless been possible to observe a difficulty in achieving an acceptable level of repeatability in the positioning. Above all, this problem has been observed at high machine speeds. The indexing principle described in EP 1 249 399 functions excellently, but for certain machine construction and certain speeds the idea needs to be further developed in order to be able to meet the requirements for correct positioning within very narrow positioning tolerances.